1. Field of the Invention
The present invention relates to a comparator and an optical-disc recording/reproduction apparatus. More particularly, the present invention relates to a recorded-information detection circuit employed in a RF (radio-frequency) signal processing system of an optical-disc recording/reproduction apparatus to serve as a detection circuit for determining whether or not a signal is being supplied to a VGA (variable-gain amplifier).
2. Description of the Related Art
The existing optical-disc recording/reproduction apparatus employs a recorded-information detection circuit for distinguishing recorded and unrecorded areas in an optical disc from each other and for detecting a signal defective portion inadvertently created in the optical disc due to, among others, dusts and/or flaws.
A typical configuration of the recorded-information detection circuit is disclosed in Japanese Patent Laid-open No. Hei 7-334918 whereas an optical-disc recording/reproduction apparatus employing this recorded-information detection circuit is disclosed in documents such as Japanese Patent No. 3458502.
FIG. 6 is a block diagram showing an RF-signal processing system employed in the existing optical-disc recording/reproduction apparatus to serve as a circuit which includes an AGC (automatic gain control) loop. A recorded-information detection signal is used in the AGC loop to serve as a signal for controlling the RF-signal processing. To put it in detail, the recorded-information detection signal is typically used for carrying out hold/reset control of the AGC loop and hold/reset control of a PLL (phase lock loop) circuit for data clock recoveries.
For the reason described above, the recorded-information detection signal is fetched from the front stage of the AGC loop and a detection circuit is provided separately from a main signal processing system following the AGC loop to serve as a circuit for carrying out recorded-information detection processing.
In the mean time, a series of efforts made to miniature semiconductor processes in recent years by applying smaller-size design rules has been serving as a power to drive the replacement of the existing analog-signal processing with digital-signal processing which is expected to serve as processing to be also applied to the recorded-information detection circuit as well.